This invention relates to manual tracking systems having multipower displays and in particular to such systems involving a switchover from proportional to proportional-plus-integral control of the sensor upon a change of optical magnification.
Manual tracking systems employing multipower displays require switching of the gain of the sensor controller to offset optical magnification changes. Specifically, as the display is switched from low to high magnification there must be a simultaneous offsetting reduction of the controller gain in order to maintain stable control of the sensor. This gain reduction causes several problems including a step change in commanded sensor line of sight rate, often causing loss of target track; reduction in the dynamic range of the sensor line of sight rate control, thereby precluding engaging targets when large line of sight rates are involved; and the presence after switchover of a nonneutral controller position and force, which causes inaccurate target tracking. Current systems address these problems, but do not wholly solve them, by providing a subsequent manual switchover from proportional to proportional-plus-integral control of the sensor. In particular, these systems require the manual switching-in of a rate-aiding parallel integrator which takes over the steady state and low frequency components of the commanded line of sight rate, thereby allowing the operator to track the target about a more neutral controller position and force while somewhat increasing the dynamic range of the controller. The integrator gain must be low enough, however, to permit gradual transfer of control from the operator to the integrator. Otherwise target tracking becomes disrupted. Consequently, the dynamic range of control, while improved, still remains restricted. In addition, the gradual transfer of control takes a relatively long time, typically five to fifteen seconds, during which time tracking is inaccurate. These systems have an additional problem in that manual switching-in of the integrator occurs at a critical moment when the operator is preoccupied with compensating for the control transients which result from the low-to-high magnification switchover, tracking about a non-neutral controller position and/or force, and continuous visual fixation on the display. Because of these factors switching of the integrator must be done by feel, which naturally leads to errors.
The following U.S. patents are representative of the prior art: U.S. Pat. Nos. 2,998,942; 3,711,046; 3,733,133; 3,829,659; and 4,038,547.